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Structural and dynamic characterization of Li(12)Si(7) and Li(12)Ge(7) using solid state NMR
Sven Dupke1, Thorsten Langer, Rainer Pöttgen
1Institute of Physical Chemistry, WWU Münster, Corrensstrasse 28/30, 48149 Münster, Germany.
Detailed NMR studies reveal high lithium ion mobility in lithium silicide Li(12)Si(7) and its germanium analog. Lithium ions exhibit significant charge, suggesting aromatic ring currents in silicon structures.
Area of Science:
- Solid-state chemistry
- Materials science
- Nuclear Magnetic Resonance (NMR) spectroscopy
Background:
- Lithium silicides are Zintl phases with complex structures.
- Understanding lithium ion dynamics is crucial for energy storage applications.
Purpose of the Study:
- To characterize local environments and lithium ion dynamics in Li(12)Si(7) and its germanium analog.
- To investigate the electronic structure and bonding in these lithium silicides.
Main Methods:
- Variable temperature static and magic-angle spinning (MAS) NMR experiments using (6)Li, (7)Li, and (29)Si nuclei.
- (29)Si{(7)Li} CPMAS heteronuclear correlation experiments.
- 2-D J-resolved, 2-D INADEQUATE, and radio frequency driven recoupling (RFDR) spectroscopy.
Main Results:
- Well-resolved lithium sites observed below 200K, with partial site averaging at higher temperatures.
- Significant electronic charge on lithium species indicated by chemical shifts up to 60 ppm.
- Evidence for aromatic ring currents in five-membered Si(5) rings.
- High lithium ionic mobilities demonstrated by motional narrowing effects in variable temperature (7)Li NMR spectra.
Conclusions:
- The study provides detailed insights into the local structure and dynamics of lithium ions in Li(12)Si(7) and its germanium analog.
- NMR results support the Zintl-Klemm-Bussmann concept for describing these compounds.
- The findings highlight the potential for high ionic conductivity in these materials.
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